Subject: Repost of minutes

From: Joe Macker <[email-masked]>
Date: Mon, 27 Aug 2001 16:03:14 -0400

ALL:
I am reposting a non word-wrapping version of the minutes.
-joe

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From: "wooighee" <[email-masked]>
Date: Tue, 28 Aug 2001 15:56:03 +0900

Hello All
    I have read several papers on the routing of ad-hoc network and
found most of them use the 300m x 1500m as the parameter for 
2 dimension area in their simulations. Why this parameter is chosed ?
Any specific reason ? Why shouldn't we use the 
1000m x 1000m or 2000m x 2000m area which
seems to be more "natural" ?

Yours Sincerely
Ghee

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From: "wooighee" <[email-masked]>
Date: Tue, 28 Aug 2001 19:08:57 +0900

Dear Mr Kwan-Wu Chin

Thank you for responding to my question instantly.

> Most probably due to the relation between number of nodes and grid size.
> If the grid-size is too vast, nodes might move to all four corners and
> thus
> out of range from each other, i.e.,  zero thru'put.  Having a smaller
> grid
> size means that there is a high chance there will be constant
> connectivity
> throughout the simulation.
>

I agree with your point of making sure that all nodes connect with each
other.

But shouldn't we consider that segragations might happen now and then in
real world model ?

And if we want to make sure that all nodes connect with each other,
why didn't the round number parameter like 1000m x 2000m
be used in the simulations ?

If I am wrong, please kindly correct me.

Thank you very much.

Yours sincerely
Wooi-Ghee, Wang

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From: Joe Macker <[email-masked]>
Date: Tue, 28 Aug 2001 10:05:13 -0400

>be used in the simulations ?

I think you see people trying to build on other's results and using other people's simulation scripts, therefore the grid replication, but the grid sizes and shapes are somewhat subjective (of course in most simulations you want some degree of connectivity and some multi-hopping to occur, the grid size, mobility model, and number of nodes are factors). Elongated rectangles may actually help some protocols perform better so its good to try other scenarios as you point out.

In short, I suggest choosing what you think makes sense for what you are examining. Don't worry too much about what other researchers did.  Although if you want to compare against "well known" past results you may need to replicate some of those scenarios.

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From: Yih-Chun Hu <[email-masked]>
Date: Tue, 28 Aug 2001 10:15:56 -0400 (EDT)

Wooi-Ghee Wang,

I'm part of the Monarch Project (http://www.monarch.cs.rice.edu/), which
started at CMU but has now migrated to the warmer climate at Rice. Perhaps
I can explain why the paper we presented at MobiCom 98 used the 300x1500
area. 

Given the speed of computers at the time (1998) and the deadline for
finishing our paper, we were unable to run simulations quickly enough with
more than 50 nodes (the computational complexity of generating and running
scenarios is at least n^2 in the number of nodes). To ensure acceptable
levels of connectivity, we needed sufficient density. A square room of the
same area (670x670), however, provides a maximum separation of less than
950m, as opposed to 1530m in the rectangular scenario we used. We
determined that scenarios run in the square room did not sufficiently
stress the protocols we were testing. 

You point out that in real life, nodes may be partitioned; however, since
one of the metrics we measured was Packet Delivery Ratio, and because
packets cannot be delivered to a destination node that is partitioned from
the source node, partitions unfairly bias towards protocols that are more
likely to retain packets waiting for partitions to heal (such as DSR) as
opposed to those likely to drop packets when partitions are present (such
as DSDV).

I hope this answers your questions.

Yih-Chun

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From: Richard <[email-masked]>
Date: Tue, 28 Aug 2001 13:23:05 -0700

Wooi-Ghee Wang,

I am glad you brought up this question, because I agree with 
you that a rectangle size of 500m x 1000m is more natural than 
300m x 1500m, and we need some standard scenarios on which to 
compare different protocols. 

It appears that the choice of 300m x 1500m was to ensure connectivity
at all times when there are only 50 nodes, and perhaps also to provide 
longer paths.  But I think that such long, narrow rectangles 
should be avoided if possible.  Here are some ways to avoid them:

1. Use more nodes. The MANET charter indicates that a few hundred
nodes should be supported.  If the simulation includes at least 100 
nodes, a rectangle size of 500m x 1000m should ensure good connectivity
(assuming the transmission radius is 250m).

2. Allow scenarios in which the network partitions, but ensure that 
all compared protocols buffer packets with no route for the same length 
of time.  I think that any protocol, including proactive ones, can
be modified to do this.  

3. In measuring packet delivery ratio, count only packets received 
within some deadline (e.g., 1 second), depending on the type of traffic.
This makes sense for real-time traffic like audio or video.

I would like to see a standard set of scenarios for comparing different 
protocols (to avoid the possibility that each person selects scenarios 
that make their protocol look good). These should include both sparse 
topologies (likely to partition) and dense topologies, and should include 
different numbers of nodes (e.g., 50, 100, 150, 200) and different rectangle 
sizes (e.g., 500m x 1000m, 1000m x 2000m).

For the mobility model, most papers I have seen use the Random Waypoint 
model, so the standard set of scenarios should probably use that model.
I would prefer that obstacles be included (perhaps two square buildings), 
or perhaps random fading (as Philippe suggested).

Regards,
Richard

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From: "wooighee" <[email-masked]>
Date: Fri, 31 Aug 2001 18:31:03 +0900

Dear Mr. Yih-Chun Hu,

Thank you very much for responding instantly to my question.
I agree with most of your explanations.
However, I am wondering that in what kind of real world environment
that the parameters which you chose trying to depict ?

A 300m x 1500m space with the speed of 0-20m/s (0-72km/hr) ?
A "rectangular" park where users moving around ?
A "rectangular" room where users moving around with the average speed of
25km/hr ?
I can't really image any real implementation model that your parameters
trying to depict.

Thank you very much.

Yours sincerely
Wooi-Ghee Wang

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From: [email-masked]
Date: Fri, 31 Aug 2001 08:11:48 -0400 (EDT)

> A "rectangular" room where users moving around with the average speed of

Hmmm, have you ever received a speeding ticket while moving in your house
(:-) ... 

While we are on the subject I am chairing a session on Outrageous Opinions
at the next Mobihoc. If you have an outrageous opion ... and I know many
of you do (:-) ... please send me a short (max 50 word) abstract.

Zygmunt.
==--==-==
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Prof. Zygmunt J. Haas                    tel: +1-607-255-3454
Wireless Networks Laboratory		                  
School of Electrical Engineering         fax: +1-607-255-9072 
Cornell University
323 Frank Rhodes Hall			e-mail: [email-masked]
Ithaca, NY 14853			
U.S.A                             http://www.ee.cornell.edu/~haas/wnl.html
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From: Yih-Chun Hu <[email-masked]>
Date: Fri, 31 Aug 2001 13:54:30 -0400 (EDT)

Wooi-Ghee Wang,

>that the parameters which you chose trying to depict ?

I agree that it's at least a bit whacked to move around a 300m x 1500m
space with speeds approaching 40mph. Please remember, however, what we're
trying to do: compare the ability of various protocols to route packets
successfully. If the movement speeds we used were those of people walking
around (0-2m/s), the difficulty of routing would be such that there would
be little to compare between the four protocols we tested.

In real life, speeds approaching 40mph are not unimaginable; we have put
on two live demos showing traffic passing between cars moving at speeds of
up to 20-25mph, using routes as long as 6 hops.

The speed/range ratio isn't particularly unrealistic, and of course the
speed/length ratio was constrained by our requirement of reasonable
density and computing requirements, as described in my previous email.

Even with so many simulations being conducted in the area, I don't know
that I've yet seen a paper claiming to have a realistic movement model.
Models used for evaulating cellular handoff schemes can't be used in 
ad hoc networks because they tend to be discretized into cell-to-cell
transitions, while our models require an exact location in order to
determine the signal and interference at a receiver.

Again, I hope this answers your question...

Yih-Chun